Hadal zone

The hadal zone, also called the hadopelagic zone, is the deepest part of the ocean. It is found in oceanic trenches. It lies about 6 to 11 kilometers below sea level, in long, narrow valleys.

Even though it covers only a small part—less than 0.25%—of the world's seafloor, the hadal zone has more than 40% of the ocean's depth. Most of these deep places are in the Pacific Ocean, the biggest and deepest ocean area.

Terminology and definition

The hadal zone is the deepest part of the ocean. People used to think it was just part of the abyssal zone. In the early 1950s, scientists found that life changes a lot at very deep levels, between 6,000 and 7,000 meters. In 1956, Anton Frederik Bruun suggested calling this deepest part the "hadal" zone. He named it after Hades, the ancient Greek god of the underworld. Most of the hadal zone is found in deep subduction trenches.

Depths deeper than 6,000 meters are usually in oceanic trenches. Some trenches are not deep enough to be hadal. Many people use 6,000 meters as the limit, but some scientists suggest using 6,500 meters instead. Animals in the hadal zone can be split into two groups: those that live on or near the bottom, and those that swim in the water above.

Ecology

The deepest parts of the ocean, called trenches, are some of the least explored places on Earth. These areas have no sunlight, very cold temperatures, and very high pressure. Most of the animals there eat bits of dead material falling from above. Scientists have found over 400 different kinds of animals living in these deep trenches. Some of these animals are bigger than we might expect, while others are very small.

Even though it’s very deep, many types of animals still live there, like fish, sea cucumbers, and tiny worms. These animals have special ways to survive the high pressure and cold. Only a few kinds of fish live in the deepest parts, but some bigger animals, like certain squids and worms, can be found even deeper.

Conditions

The hadal zone is the deepest part of the ocean. Special bacteria are the main source of food there. These bacteria can live by using hydrogen and methane from reactions between rocks and seawater, or hydrogen sulfide from cold seeps. Some bacteria live inside small ocean creatures.

This zone is deeper than 6,000 meters (20,000 feet). The deepest known point is 10,911 meters (35,797 feet). There is no light, and the pressure is very high—over 1,100 times normal air pressure. This makes the area very hard to explore.

Exploration

Exploring the hadal zone needs special tools that can handle very high pressure. Some simple tools have been used to learn about the basic life there. Both people inside and robots outside can help study these deep places. Robots can be controlled from ships or move on their own. Cameras and tools on these robots let scientists watch and collect samples of mud and living things. Sadly, some robots have broken apart under the pressure of the deep sea. The HROV Nereus is thought to have broken apart at a depth of 9,990 meters while exploring the Kermadec Trench in 2014.

Notable missions

In 1960, two explorers named Jacques Piccard and Don Walsh made the first trip to the deepest part of the ocean, called Challenger Deep. This place is in the Mariana Trench. They used a special underwater vehicle named Trieste and went down 10,911 metres.

Later, in 2012, a filmmaker named James Cameron also went to the bottom of the Mariana Trench alone. He used a vehicle called Deepsea Challenger and reached a depth of 10,908 metres. This was just a little less deep than Piccard and Walsh went.

Also in 2012, a Chinese underwater vehicle named Jiaolong went down 7,020 metres in the Mariana Trench. This made it one of the deepest research vehicles ever made.